Explicit type annotation in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with an explicit type annotation.

Swift

var age: [1] = 25

Drag options to blanks, or click blank then click option'

AString

BBool

CInt

DDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using String instead of Int for numbers.

Forgetting to specify the type after the colon.

The variable age is declared with the explicit type Int to hold integer values.

2fill in blank

medium

Complete the code to declare a constant with an explicit type annotation.

Swift

let pi: [1] = 3.14159

Drag options to blanks, or click blank then click option'

ADouble

BInt

CBool

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int for decimal numbers causes errors.

Using String instead of a numeric type.

The constant pi is declared as a Double because it holds a decimal number.

3fill in blank

hard

Fix the error in the code by adding the correct explicit type annotation.

Swift

var isActive: [1] = true

Drag options to blanks, or click blank then click option'

ABool

BString

CInt

DDouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int or String for boolean values.

Omitting the type annotation when it is required.

The variable isActive holds a true/false value, so it must be of type Bool.

4fill in blank

hard

Fill both blanks to declare a variable with explicit type annotation and assign a string value.

Swift

var name: [1] = [2]

Drag options to blanks, or click blank then click option'

AString

B"John"

CInt

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int as the type for text.

Assigning a boolean value instead of a string.

The variable name is declared as a String and assigned the string value "John".

5fill in blank

hard

Fill all three blanks to declare a constant with explicit type annotation and assign a boolean value.

Swift

let isEnabled: [1] = [2] // [3]

Drag options to blanks, or click blank then click option'

AInt

BBool

Ctrue

DThis declares a boolean constant

Attempts:

3 left

💡 Hint

Common Mistakes

Using Int as the type for boolean values.

Putting the boolean value in quotes making it a string.

The constant isEnabled is declared as a Bool and assigned the boolean value true. The comment explains the declaration.

Practice

1. What does explicit type annotation in Swift do?

easy

A. It removes the need to declare variables.

B. It automatically converts types during runtime.

C. It tells the exact data type of a variable or constant.

D. It makes the program run faster by skipping type checks.

Solution

1. Step 1: Understand the purpose of explicit type annotation

   Explicit type annotation is used to specify the exact data type of a variable or constant in Swift.

2. Step 2: Compare with other options

   The other options describe behaviors unrelated to explicit type annotation, such as automatic conversion, removing the need to declare variables, or performance improvements.

3. Final Answer:

   It tells the exact data type of a variable or constant. -> Option C

4. Quick Check:

   Explicit type annotation = exact data type [OK]

Hint: Explicit type annotation means writing the type after the variable name [OK]

Common Mistakes:

• Thinking it changes runtime behavior
• Confusing with type inference
• Believing it speeds up code execution

2. Which of the following is the correct syntax for explicit type annotation in Swift?

easy

A. var age: Int = 25

B. var age = Int: 25

C. var age Int = 25

D. var age = 25: Int

Solution

1. Step 1: Recall Swift syntax for explicit type annotation

   The correct syntax is to write the variable name, then a colon, then the type, then an equals sign and the value.

2. Step 2: Check each option

   var age: Int = 25 matches this syntax exactly. The other options have misplaced colons or missing punctuation.

3. Final Answer:

   var age: Int = 25 -> Option A

4. Quick Check:

   Variable name : Type = value [OK]

Hint: Remember: variableName: Type = value [OK]

Common Mistakes:

• Putting colon after the value
• Missing colon between name and type
• Using equal sign before type

3. What will be the output of this Swift code?

let pi: Double = 3
print(pi)

medium

A. Error: Cannot assign Int to Double

B. 3

C. 3.00

D. 3.0

Solution

1. Step 1: Analyze the type annotation and assigned value

   The variable pi is declared as a Double but assigned the integer 3. Swift converts the integer 3 to 3.0 automatically.

2. Step 2: Understand print output for Double

   Printing a Double with value 3 prints as 3.0 by default.

3. Final Answer:

   3.0 -> Option D

4. Quick Check:

   Double 3 prints as 3.0 [OK]

Hint: Assigning Int to Double converts to decimal automatically [OK]

Common Mistakes:

• Expecting a compile error
• Thinking print shows integer 3
• Confusing Double formatting

4. Identify the error in this Swift code:

var name: String = 123
print(name)

medium

A. Type mismatch: cannot assign Int to String

B. Variable name is a reserved keyword

C. Missing explicit type annotation

D. No error, prints 123

Solution

1. Step 1: Check the declared type and assigned value

   The variable name is declared as String but assigned an integer 123, which is a type mismatch.

2. Step 2: Understand Swift's type safety

   Swift does not allow assigning an Int to a String variable, causing a compile-time error.

3. Final Answer:

   Type mismatch: cannot assign Int to String -> Option A

4. Quick Check:

   Type mismatch error = Type mismatch: cannot assign Int to String [OK]

Hint: Check if assigned value matches declared type exactly [OK]

Common Mistakes:

• Assuming implicit conversion from Int to String
• Ignoring type mismatch errors
• Thinking variable names are reserved keywords

5. You want to store a list of ages as integers but accidentally write:

var ages: [String] = [20, 25, 30]

What is the best fix using explicit type annotation?

hard

A. Change to var ages = ["20", "25", "30"]

B. Change to var ages: [Int] = [20, 25, 30]

C. Remove type annotation and write var ages = [20, 25, 30]

D. Change to var ages: Int = [20, 25, 30]

Solution

1. Step 1: Identify the mismatch between type and values

   The variable ages is declared as an array of Strings but assigned integer values, causing a type mismatch.

2. Step 2: Fix by matching type annotation to actual data

   Changing the type annotation to [Int] matches the integer values in the array.

3. Final Answer:

   var ages: [Int] = [20, 25, 30] -> Option B

4. Quick Check:

   Array type matches element types [OK]

Hint: Match array type annotation to the element types [OK]

Common Mistakes:

• Changing values to strings unnecessarily
• Removing type annotation without understanding
• Using single Int type for array